Gaseous conduction device



March 1, 1932. E, CHARLTON 1,847,927

GASEOUS CONDUCTION DEVICE Filed July 17, 1924 Inventor- Ernest E.Char-Lton I-ILs Attorney Patented Mar. 1, 1932 I UNITED STATES PATENT OFFICE ERNEST E. CHARLTON, OF SCHENECTA DY, NEW YORK, ASSIGNOR TO Gm m COMPANY, A. CORPORATION OF NEW YORK GASEOUS CONDUGTION DEVICE Application med July 17, 1824. Serial No. 780,040.

The present invention relates to electric discharge devices which operate by the ionization of a gas, and it is the object of my 1nvention to improve the eificiency and reliability of these devices.

Gaseous conduction devices, such as glow discharge lamps and rectifiers, which are charged with an inert gas, such as neon or helium, operate by virtue of the ionization N1 of the gas when a sutficiently high voltage is impressed upon the electrodes.

In order to reduce to a minimum the voltage necessary to produce this discharge between the electrodes, it has been found advantageous to introduce small amounts of alkali metals, such as sodium or potassium, into the bulb. These metals being highly oxidizable combine with deleterious gases which may be evolved from the walls of the bulb during operation.

In a gas discharge rectifier for alternating current the presence of alkali metal at an appreciable vapor pressure is apt to increase the likelihood of undesired reverse discharges in the rectifier and in a gaseous glow lamp the alkali metal tends to obscure the light emission b the formation of a film on parts of the bul surface.

I have discovered that the voltage necessary for operating devices of this class may be reduced without these disadvantages by providing in the bulb together with an inert gas, an oxide of an alkali metal, preferably associated with a highly oxidizable metal 5 such as an alkaline earth metal. Apparently, the alkali metal oxide combines with hydrogen which appears to be formed by the decomposition of water vapor and also with such ases as carbon monoxide which sometimes are evolved from the electrodes during the operation of the device. The novel features of my invention will be pointed out with greater particularity in the appended claims.

The accompanying drawings show for illustrative purposes two forms of discharge devices to which my invention is applicable. Fig. 1 shows partly in section an ionization rectifier for alternating current and Fi 2 Thows in perspective an ionization g ow amp.

The rectifier shown in Fig. 1 comprises a bulb consisting as usual of glass and containing anodes 2, 3 which have a small exposed surface and are respectively sur- 6! rounded by housings 4, 5. The latter are connected together and form a single cathode having relatively much larger surface than either of the anodes. Ordinarily, the surface of the cathode is more .0 than 300. times as great as the surface of either of the anodes. Tl1'e anodes 2, 3 conveniently are constituted by the exposed ends of wires 6, 7 passing through the glass tubes 8, 9 which form an extension of 66 the glass stem 10. Although these wires may consist of any metal whlch is not readily vaporizable by electric discharges, I prefer to employ tungsten as it is readiy sealed into a hard glass, such as a sodium-magnesium borosilicate. The cathode conveniently consists of nickel. The anode conductors 6, 7 together with the cathode conductors 11, 12 are sealed to the external contacts 13 of a bayonet type base 14. I

In the manufacture of the device, the bulb 1 is first baked out at a temperature of about 450 C. to remove water vapor and is evacu-. ated in the usual manner (the tubulature through the base not being shown). After 80 the evacuation a small amount of an alkali metal, preferably caesium, is introduced into the bulb 1 and this metal is oxidized by the admission of a small quantity of oxygen and warming of the bulb to somewhat above room 35 temperature, say to about 50 C. The excess oxygen is pumped out. Instead of caesium other alkali metal may be used in the preparation of the device, but among these metals caesium and rubidium are preferred. Prefer- .9

-It can ably a small quantity of alkaline earth metal such as ma esium or calcium, is deposited on the bulb fore the gas filling is admitted. This'metal may be aifixed to one of the electrodes, (conveniently the cathode as indicated at 15) prior to the assembly of the device. be va orized by introducing'the device into a high requency electromagnetic field.

The bulb is finally charged with an inert gas, preferably helium or neon, at a pressure WlllCh may vary between the limit of about 5 to 80 millimeters of mercury. A' pressure of about 19 millimeters of mercury is preferred. Other gases of the rare gas group may be used but either helium, or a mixture of helium and neon is preferred. By the chemical affinity of the alkaline earth metal and the alkali metal oxide for such gases as hydrogen and carbon monoxide, the voltage drop in the rectifier during operation is lowered about The large ex osed surface obtained by the condensation o the alkaline earth metal and the oxide of the alkali metal on the inner surface of the bulb materially enhances the reactivity of these metals for deleterious gas. As metals of the alkaline earth group have an-inappreciable vapor pressure at the operating temperature of a gaseous glow device, the resence of this metal will not cause undesire electric discharges. In some cases, instead .of introducing the alkali metal and the alkaline earth metal separately, a mixture of a halide of an alkali metal, as, forexample, caesium chloride together with an excess of alkaline earth metal is applied upon the electrode or other convenient place. This mixture may be compressed into the form of a small pellet. When this mixture is heated, a reaction takes place evolving the alkali metal in the elemental state. Continued heating, therefore, causes both the alkali metal and alkaline earth metal to be vaporized and to be deposited upon the inner surface of the bulb. When oxygen is admitted and the bulb is warmed, the alkali metal is oxidized, but if care is taken not to raise the temperature much above 50 C. the alkaline earth metal is not appreciably oxidized. Some alkali metal is likely unavoidabl to remain unoxidized. The uncombine oxygen then is removed and finally the inert gas is introduced as above described. Certain structural features in the rectifier shown in Fig. 1 whereby discharges between the anodes are inhibited by the shielding effect'of the cathode are claimed in my copendin application, Serial No. 726,638 filed herewith My invention also may be applied with advantage to the production of gaseous glow lamps. In the glow lamp shown in Fig. 2 the electrodes 17 18 are constituted ofplates of iron, nickel, molybdenum, aluminum or other suitable material, which; is not appreciably vaporized at the operating temperature of such a lamp. The electrodes are connected as usual to leading-in conductors 19, 20 which are sealed into a glass stem 21 and are joined by screws 22, 23 to the electrodes 17, 18. The e ectrodes are separated by a sheet 24: of refractory dielectric material for example fused quartz or hard glass. A small pieceof insulation 25, for example mica, is provided to insulate the conductor 19- from the electrode 18, the screw 22 contacting with the electrode 17. The drawings also show supporting anchors 26, 27 for the electrodes but, of course, these structural features are shown for illustrative purposes only and have no particular bearing upon my invention.

In the glow lamp as well as in the rectifier, the bulb is first freed from water vapor by baking in the usual manner and it is then exhausted to a high vacuum. The alkali metal, either alone or together with the alkaline earth metal, may be introduced by either of the methods described in connection with Fig. 1. Forexample, a ellet consisting of a mixture of alkali metal alide and an excess of alkaline earth metal, for example, caesium, chloride and magnesium, may be placed within a heater 28 consisting of a spiral refractory filament, tungsten, for example, which is connected between the leading-in conductors 19, 20. Upon the application of heat the reaction occurs, above indicated, causing some of the alkali metal to be vaporized. The filament may be finally burned out by passing an excess current through the same. A

. quantity of oxygen then may be admitted by a tube 29, connections to the vacuum pum being closed by a cock 30. The alkali metfi is oxidized at a temperature at which the alkaline earth metal is not appreciably oxidized. The excess oxygen is pumped out. Neon or other rare gas, or rare gas mixtures, then are admitted at a desired pressure varying usuall between a few millimeters and a few centimeters of mercury, depending on conditions.

In a lamp, to insure transparency of the bulb, the caesium or other alkali metal may be introduced as a vapor from an external source, and then oxidized by the introduction of oxygen gas before introducing the neon, or other gas filling.

What I claim as new and desire to secure by Letters Patent of the United States, is,-

1. The method of preparing a gaseous low device which consists in evacuating a ulb introducing a small amount of alkali metal into said bulb, admitting a small amount of oxygen, heating the bulb to a temperature at which oxidation of alkali metal occurs, removing the uncombined oxygen, introduc' an alkaline earth metal into said bulb an finally providing the bulb with a, desired gaseous filling.

2. The method of preparing a gas filled glow discharge device which consists in evacuating a container provided with suitable electrodes, introducing a small amount of alkali metal into said container, admitting suflicient oxygen to convert said alkali metal to an oxide, removing excess of oxygen and introducing a rare gas at a pressure material- 1y less than atmospheric pressure, together with a material which is capable of combining with undesired gases and has an inappreciable vapor pressure at the operating temperature of said device.

In witness whereof, I have hereunto set my hand this 16th dafif Jul 1924.

EB ST CHARLTON. 

